1. Field of the Invention
The present invention is directed to repairing failed gravel pack screens in an oil and/or gas well. More particularly, one embodiment of the invention is directed to repairing the screen by pumping an ultra-lightweight or neutrally buoyant resin coated material into the screen into the hole(s) in the screen and into any void behind the screen. Any excess resin coated material is subsequently removed from the central passageway of the screen. Other embodiments of the present invention involve controlling sand production in cased wells.
2. Description of the Related Art
One problem facing the oil and gas industry is preventing reservoir sand from being produced with the hydrocarbons into the wellbore, which can build up and restrict hydrocarbon production. An increasing number of reservoirs are being drilled horizontally and many of these wells often require sand control measures to prevent the buildup of sand beds in the well. To prevent and control reservoir sand, a mechanical filter may be placed between the wellbore and the formation. The filter often consists of a media, such as gravel or sand, placed between a screen and the formation. The media is carefully sized to allow the passage of hydrocarbons from the formation, but to prevent the majority of sand and particles that constitute the rock formation from passing into the well and possibly plugging it up.
For many years, the filter system commonly used comprised of media placed between a wire screen and the formation (or casing). The screen typically includes a base pipe that, depending on the size of the openhole or casing, may typically be 3.5 inch or 4 inch in diameter, although both larger and smaller sizes are in regular use. The screen base pipe would typically have a plurality of holes (e.g., ⅜ inches in diameter) drilled through the base pipe. By way of example, 50 or 60 holes per foot may be drilled in the base pipe. The base pipe gives the screen its strength. A plurality of ribs are welded longitudinally along the outer diameter of the base pipe. A wire is then wound around the outer diameter of the base pipe and ribs, the ribs generally provide a small standoff between the wire and base pipe. As the wire is wrapped around the base pipe, the space between successive wraps is sized to be smaller than the filter media, such as gravel, sand, or ceramic shapes placed between the screen and the reservoir rock or casing. Other configurations using wire mesh layers wound around a perforated base pipe are also in common use.
Clean, approximately spherical sand has been one type of media used to prevent the flow of larger particles from the formation to the wellbore. The screen is sized to effectively hold the sand in place against the formation. Properly packing the sand behind the screen can be challenging especially in long horizontal wellbores and could lead to problems with the effectiveness of the filter system. One method of packing the sand behind the screen is done by pumping water, sometimes with a polymer, to circulate the sand down behind the screen and allowing the sand to pack off at the bottom of the screen and formation interface while taking liquid returns through the screen and back to the surface. Gradually the packed sand builds up behind the screen until a uniform, annular sand pack is created between the screen and the formation. An alternative method to create the media sand pack is just pumping the sand and water into the annular cavity between the screen and formation and then squeezing the annular area and letting the liquid just disappear off into the formation.
The sand may not be uniformly compacted in the annular area regardless of what method is used. Achieving a uniformly compacted media behind a screen is sometimes difficult. For example, the screen may not be fully centered within the wellbore, there may be an area that takes fluid more readily than another part of the open hole sections, or there may be excessive liquid lost to the formation. Each of these can result in the sand behind the screen not being perfectly compacted and consolidated.
After the media is in place the well is put into production and reservoir fluids start flowing out of the rock formation through the annular area of filter media, through the screen, and up to the surface. There may be a significant pressure drop between the reservoir and the wellbore if the well is being drawn on to encourage the reservoir to produce. Voids may develop in the sand media if it was not uniformly distributed and compacted behind the screen. The hydrocarbons will preferentially flow to these voids due to there being less resistance than other portions of the media possibly creating a flow channel, which also provides for a higher velocity of flow. The absence of the media also permits the flow of very small (i.e. fine), reservoir particles through the channel.
These “fine” particles travel close to the same velocity as the hydrocarbons and over time these “fine” particles can erode a hole through the screen. A hole in the screen allows larger formation sand particles to be produced through the hole and deposited into the wellbore. Eventually, the sand build up may reach a point that it impedes production until the wellbore is cleaned out. After the cleanout of the wellbore, the sand control system preferably needs to be repaired to prevent a repeat of this problem.
Traditionally a repair would mean removing the screen and filter media and reinstalling a complete new filtering system. This process is very expensive due to the rig costs required to remove the screen and re-install a new screen. The cost also varied depending on how long the screen was. Due to the great expense in this process, a well operator had to determine how many reserves were potentially left in the well to evaluate whether the removal and repair of the screen was an economical procedure. One potential solution to fixing the screen that was not as costly was to run another screen inside the existing screen.
Although inserting a replacement screen within an existing screen may not be as expensive, it also has it limitations. Gravel pack completions on horizontal wells can extend over a thousand feet or longer and rectifying a failure using an insert screen over the whole length can be prohibitively expensive.
In a horizontal well, the existing filter may extend over thousands of feet long and the screens used in these applications can cost hundreds of dollars per foot. Thus, it may not be economical to insert a 2000 foot screen when only a small portion of the existing screen has been damaged. Furthermore, the rig and consequential workover costs associated with placing an insert screen inside a failed screen can also be significant.
Instead of inserting a replacement screen along the whole length, one possible solution is to install an insert screen across the damaged area. This could be possible if there was a technology available to readily locate where the existing screen had failed. The failure normally occurs in the wire or mesh behind the base pipe making failure location especially difficult. Because the screen itself is porous, it allows reservoir fluid to flows in and across the screen further compounding the difficulty of locating the failure. Presently there is no effective technology that may be run into the well to easily determine where the screen failure is located.
There are other limitations of whether insert screens may be used. For example, the size of the well may be too small to accommodate the insertion of another screen. An insert screen may be used as a purely mechanical screen or it may be used in conjunction with media between the existing screen and the insert. Although using media between the insert screen and the existing screen may provide better filtering capabilities it may also affect the production of the well. The use of an insert screen and filter media will normally limit the flow of hydrocarbons as now the hydrocarbons will have to flow through a smaller cross-sectional area resulting from the smaller annular ring of filter material. For the same pressure drop the flow through that smaller cross-sectional flow area is necessarily lower. Additionally, the insert screen reduces the internal diameter of the wellbore and limits options for future intervention operations.
As an alternative to installing insert screens inside a failed screen, one method to repair the failed screen is to try to squeeze resin coated sand into the screen in an effort to repair the failure. It was speculated that the resin coated sand would penetrate through the failure and into the void in the media behind the failure. The resin coated sand would then set up and harden preventing further sand ingress. The success of this method has typically been low and is often employed as a last resort.
One reason for the limited success is that resin coated sand is generally over 2.5 times heavier than water. The resin coated sand is mixed with water and pumped into the hole down to the screen. While the water will flow through the screen, in a vertical well the resin coated sand tends to fall into the bottom of the hole instead of penetrating into the screen and void behind the screen because the resin coated sand is heavier than the water. In a horizontal well, it can be even more difficult to repair a hole on the high side of the well. Gravity causes the resin coated sand to collect at the bottom side of the screen because it is heavier than the water or fluid it is pumped with.
In some instances, a cased well may not include a mechanical sand control system, such as a filter comprised of media and a screen, as discussed above. During the production of hydrocarbons the formation may begin to produce sand along with the hydrocarbons, which enters the cased well because no mechanical sand control system is present. The sand can build up within the well restricting the production of hydrocarbons as discussed above. It would be beneficial to provide a short term solution to control the production of sand providing for the production of hydrocarbons while a rig is procured to install a mechanical sand control system within the well. Alternatively, it may be beneficial to provide a sand control system that prevents the production of sand and that may be established within the cased well without the need of a rig. The sand control system may include a material that bridges within the perforation tunnels of the well. Such a sand control system may be more cost effective than the traditional mechanical sand control systems.
In light of the foregoing, it would be desirable to provide a method of repairing a gravel pack failure downhole even if the failure is located on the high side of a deviated or horizontal well. It would also be desirable to provide a material that is able to penetrate the screen failure and the void behind the failure to build up and prevent further ingress of reservoir sand and formation particles. It would be desirable to provide a repair material that is able to locate a failure in a downhole screen. It would further be desirable to provide a repair material that may repair a failed screen such that excess repair material may be readily removed from the wellbore. It would also be desirable to provide a material that may be used as a temporary sand control system within a cased well until a mechanical sand control system can be installed into the cased well. It would further be desirable to provide a method of squeezing a neutrally buoyant material into perforation tunnels in a cased well that may prevent the production of sand into the cased well.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the issues set forth above.